Escherichia coli cells are normally impermeable to the antibiotic actinomycin D1 which inhibits DNA-dependent RNA synthesis2 and the consequent inducible enzyme synthesis. Leive has shown that after treatment with EDTA, E. coli cells are more susceptible to actinomycin D 3 and that a lipopolysaccharide is released from the cell wall 4. We have confirmed the observation5 that E. coli cells also release a lipopolysaccharide into the medium after infection with the small filamentous phage M13 (unpublished results). Here we show that M13 infected cells are permeable to actinomycin D. It should be noted that M13 infected cells continue to grow and multiply while releasing progeny phage particles 6,7.
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